Virtual machine is slow

Hello @Justine Yamane,

Thank you for reaching out Q&A forum.

Run these immediately on the VM to get a snapshot:

Linux

bash

# Overall CPU, memory, load average
top -bn1 | head -20

# CPU per core
mpstat -P ALL 1 3

# Memory
free -h

# Disk I/O — what's consuming it
iostat -xz 1 5

# Top disk I/O by process
iotop -o -b -n 3

# Network
sar -n DEV 1 5

# What processes are consuming most resources
ps aux --sort=-%cpu | head -20
ps aux --sort=-%mem | head -20

Windows

powershell

# Quick resource snapshot
Get-Process | Sort-Object CPU -Descending | Select-Object -First 20
Get-Process | Sort-Object WorkingSet -Descending | Select-Object -First 20

# Disk I/O
Get-Counter '\PhysicalDisk(*)\Disk Bytes/sec'
Get-Counter '\Processor(_Total)\% Processor Time'
Get-Counter '\Memory\Available MBytes'

Use Azure's Built-in Diagnostics

Performance Diagnostics Extension

In the portal: VM → Diagnose and Solve Problems → Performance Diagnostics

This runs automated checks and gives you a report on:

• CPU bottlenecks
• Memory pressure
• Disk throttling
• Network issues
• Top resource-consuming processes

Azure Monitor / Log Analytics

If you have the Azure Monitor Agent installed:

kusto

// Top CPU consuming processes over last hour
Perf
| where TimeGenerated > ago(1h)
| where CounterName == "% Processor Time"
| where InstanceName != "_Total"
| summarize avg(CounterValue) by Computer, InstanceName
| top 20 by avg_CounterValue desc

kusto

// Disk latency
Perf
| where CounterName == "Avg. Disk sec/Read" or CounterName == "Avg. Disk sec/Write"
| where TimeGenerated > ago(1h)
| summarize avg(CounterValue) by CounterName, bin(TimeGenerated, 5m)
| render timechart

If this answers your query, do click Accept Answer and Up-Vote for the same. And, if you have any further query do let us know.

Hello Justine,

Thank you for reaching out regarding the performance concern with your virtual machine.

Slowness in an Azure VM can occur due to multiple factors such as high resource utilization, storage performance limits, network latency, or changes in workload behavior. To effectively troubleshoot this issue, it is important to identify where the performance bottleneck is occurring.

We recommend starting with a review of VM resource utilization using Azure Monitor. Please navigate to Azure Portal → Virtual Machine → Monitoring → Metrics and review CPU, memory, disk, and network usage during the time when the issue was observed. Consistently high CPU usage may indicate that the workload exceeds the VM’s current capacity, while high memory utilization can lead to paging and degrade performance.

Documentation: Monitor virtual machines in Azure

Next, please check disk performance metrics such as latency, IOPS, and throughput. Disk performance is a common cause of slowness, especially for workloads with heavy read/write operations. Each VM and disk type has defined IOPS and throughput limits, and reaching these limits can result in slower response times. You can review the disk configuration from VM → Disks.

Documentation: Virtual machine and disk performance

It is also important to verify the processes running inside the virtual machine. In some cases, the Azure platform metrics may appear normal, but a specific application or background process within the OS might be consuming high resources.

For Windows VMs, you can check Task Manager, and for Linux VMs, commands such as top or htop can help identify resource-intensive processes.

Additionally, we recommend running Azure Performance Diagnostics (PerfInsights), which is a diagnostic tool designed to collect and analyze detailed performance data. It helps identify issues related to CPU contention, memory pressure, disk latency, and OS-level bottlenecks by generating actionable insights.

Documentation: Use performance diagnostics in Azure Monitor to troubleshoot VM performance problems

Troubleshoot Azure virtual machine performance on Linux or Windows

Finally, please review whether the current VM size aligns with your application requirements. If the workload has increased over time, the existing VM SKU may not be sufficient in terms of CPU, memory, or disk performance. In such cases, resizing the VM to a higher SKU or an appropriate VM family may help improve performance.

Reference Documentations: Change the size of a virtual machine

Run performance diagnostics reports on Azure virtual machines

Slow Azure VM Start operations when extensions are "Failed"

Hope this helps! Please let me know if you have any queries in comments.

Welcome to Microsoft Q&A

Hello @Justine Yamane

Microsoft has a built-in tool that will figure it out for you,

Here is the easiest way to troubleshoot:

Open your Virtual Machine in the Azure Portal.

Scroll down the left menu until you find Performance diagnostics (under the Help/Troubleshooting section).

Click the button to Install and Run a diagnostic test.

1. Choose the "Performance Analysis" option and let it run for a few minutes while the machine is acting slow.
2. Once it finishes, it will generate a very easy-to-read report. It will tell you exactly what is slowing the machine down. For example, it might tell you "Your disk is maxed out" or "An antivirus program is using 99% of your CPU."

If the report shows you are simply maxing out the machine's limits, you will just need to click "Size" on the left menu and upgrade the VM to a slightly larger size!

😊 If my answer helped you resolve your issue, please consider marking it as the correct answer. This helps others in the community find solutions more easily. Thanks!